<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
    <style>
      div {
        width: 400px;
        height: 400px;
        border: 2px solid black;
        margin: 0 auto;

        /* border-radius: 200px; */
        border-radius: 50%;

        /* border-top-left-radius: 100px;
        border-top-right-radius: 50px;
        border-bottom-left-radius: 20px;
        border-bottom-left-radius: 10px; */

        /* 椭圆 */

        /* border-top-left-radius: 100px 50px;
        border-top-right-radius: 50px 20px;
        border-bottom-left-radius: 20px 10px;
        border-bottom-left-radius: 10px 5px; */

        /* 复合属性 */

        /* border-radius: 100px 50px 20px 10px / 50px 20px 10px 5px; */
      }
    </style>
  </head>

  <body>
    <div></div>
  </body>
</html>
